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What is a "universal" disc rotor? One that is compatible with all types of brake pads?

universal rotor

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  • My only thought would be that it is compatible with both center lock and 6 bolt style mounts, or that it comes with an adapter to do so. Do you have an example? All disc brake rotors should be compatible with any pads. – Nate W Jan 12 at 0:13
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    @NateW with regards to “All disc brake rotors should be compatible with any pad”, Shimano specifically state to only use resin pads with ice tech rotors. Although yes technically you could use a metal pad, it’s not advised on other forums due to heat build up and rotors warping. – Dan K Jan 12 at 6:35
  • @Nate W. The picture shows a 6-hole rotor without adapter. It is on a bicycle shop's e-tail website. – Tim Jan 12 at 12:37
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    @MaplePanda MP is right -- some Shimano IceTech rotors are compatible with metal as well as resin pads, SM-RT99-A for example. – Armand Jan 12 at 20:49
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    @Tim Of course, the only definitively safe option is to use Shimano rotors, but you will have absolutely no issues if it says Shimano pads are good. – MaplePanda Jan 13 at 1:25
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Every brake manufacturer recommends only using their own rotors, so this is another case where the answer depends very much on who you ask.

In general, here is where rotor cross-compatibility can go wrong:

  • Some inexpensive Shimano rotors have less hardening and are designated "resin only." They in fact wear very fast if a metallic or semi-metallic pad is used.
  • Magura rotors are 2mm thick and more or less everyone else's are 1.8mm. Using a thicker rotor than a caliper is designed around, along with unworn pads, could get you into situations where you don't have enough air gap to play with even with the pistons all the way in. Such issues come up rarely in practice however.
  • Different calipers can place the size and location of the pad contact patch on the rotor a little differently. It seems like in practice there is not a ton of variance, but there is some. Someone trying to design a universal rotor would be trying to make it big enough that the top of the pad on any caliper never overhangs the rotor, but the top of the rotor can never interfere with any caliper.

The main question with the idea of a universal rotor design is whether, given an on-spec location of the brake mounts, is there a magic number for the exact outside diameter needed in the last point. I don't know the answer to that. But for practical purposes, all of the above issues are rare, most rotors are designed to capture some aftermarket sales as generic repair parts, and it's all pretty cross-compatible as long as it's not resin-only or Magura.

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    In this specific case, I believe the brand does not sell brake calipers/assemblies, but just rotors, pads and other consumables. They wish people to buy their parts as replacements to use with Shimano and other brakes, so "universal" also acts psychologically to reassure the purchaser that the part will work on their system. I.e. it is partly marketing as well as technical. – Armand Jan 12 at 20:36
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    If the rotor isn't symmetrical, make sure you mount it with the correct side facing out. There's usually a little arrow indicating the direction of rotation. – Armand Jan 12 at 20:42
  • Ceramic pads (which IME are resin bonded) seem to cause far worse rotor wear than metal pads. I don't know if any rotors are specifically intended for ceramic. I didn't even know about ceramic pads until the bike shop put them on, and usually use metal. – Chris H Jan 13 at 6:43
  • There can also be issues with two-piece rotors not clearing the brake pads. This has come up for me with shimano ice-tech rotors and BB7 brakes. The issue is that the thicker aluminum part of the rotor clicks against the steel backing part of the brake pad that sticks out "below" the brake. – Fred the Magic Wonder Dog Jan 14 at 1:50
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Another subtle issue is the spacing of the vents. Ideally the pad will always contact the same amount of rotor, but if the pad size doesn't match the period of the vent pattern breaking can be uneven. This mostly seems to be an issue with fairly gentle braking.

Imagine a rotor with purely radial vents accounting for half the area swept by the pads. Now consider a pad the same width as two vents and the metal rib in between, or two ribs and one vent. The contact area changes periodically by a factor of two. As the contact force is constant, the braking force doesn't change by as much (under a simple picture with a constant coefficient of friction it wouldn't change at all). Both shape and dimensions are a little extreme as an example, but this was noticeable with a Shimano rotor I used with BB5-style brakes that have smaller pads than shimano use.

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